Whitey Bulger relaxes on Miami Beach on a sizzling hot day, sharing a lounge chair with his girlfriend, Catherine Greig, a gorgeous blonde in a bikini who cuddles like a cat between the crime boss’s legs. Nearby, Bulger’s partner, Stevie Flemmi, pulls on a cigarette. FBI agent John Connolly peels off twenties to pay for rum drinks as Boston businessman John Callahan, an executive with World Jai Alai, eagerly sips his. Bulger’s protege Kevin Weeks struts from the surf and joins them.

It’s the Whitey Bulger Gang, circa 1981, riding the wave of its unholy alliance with the deeply corrupted FBI. The notorious gangster is catching a break from the underworld grind, even as he mulls yet another murder, that of Callahan’s boss, the owner of World Jai Alai.

But this isn’t 1981. It’s July 11, 2014 — and it’s not Whitey Bulger, but Johnny Depp. Nor is that Catherine Greig, but Sienna Miller. John Connolly is Joel Edgerton, and so on. It’s also not Miami Beach, but our own Revere Beach, transformed magically with imported palm trees and popsicle-colored cabanas to resemble the Florida coast. This is Scene 91 in director Scott Cooper’s adaptation of “Black Mass: Whitey Bulger, the FBI and a Devil’s Deal,” a book Gerry O’Neill and I wrote that built off of years of reporting we and others did for The Boston Globe.

Since May 19, Cooper and his vast crew have been moving around the area, making a movie out of the murderous collusion between Whitey and the FBI. I was invited to the set soon after, and it was a Chelsea morning in early June, under a gray, unfriendly sky, when I first met Depp — or, I should say, Whitey. I had arrived while they were shooting a scene where Depp as Whitey, driving a Malibu, gets pulled over by a Boston police officer on the payroll of Mafia underboss Gennaro “Jerry” Angiulo. Between takes, and while the camera angle was changed, I spotted Depp standing 15 yards away conferring with Rory Cochrane, the actor playing Stevie Flemmi.

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Rory looked my way, and then Johnny did, too. Johnny waved. I looked over my shoulder, figuring he was acknowledging one of the producers behind me. But then Johnny headed in my direction, and that’s when I began to feel edgy. In blue jeans, leather jacket, tinted glasses, and a bald cap the makeup department had devised to create a high forehead and slicked-back blond hair, Johnny looked like Whitey. It was eerie, to say the least. He even moved like Whitey, with the signature swagger that Massachusetts State Police Sergeant Bob Long and his troopers first captured in surveillance photographs they took in 1980 while monitoring Whitey lording over the Lancaster Street garage near North Station.

Truman Capote once wrote an essay about visiting the set during the 1967 filming of his book “In Cold Blood,” and I wish I could compose lines as artful as his to describe the experience of seeing an actor who has brought an antagonist you know to life.

“I thought a ghost had sauntered in out of the sunshine,’’ he wrote about seeing Robert Blake for the first time portraying the killer Perry Smith. Capote said he had trouble processing the “mesmerizing reality’’ of the actor cast as Perry, because he was Perry, and that’s how it was with Johnny: He was Whitey. It was disorienting, “like a free fall down an elevator shaft,’’ as Capote put it. “The familiar eyes, placed in a familiar face, examining me with the detachment of a stranger.”

As Johnny and I talked for 10 minutes about a bunch of different things — a mutual interest in the gonzo journalist Hunter S. Thompson, for example — he maintained that menacing glare and tone, rooted in some strange place between Whitey and himself.

Most days were like that, off-balance and surreal, as actors and crew members resurrected people and places from the region’s collective past and brought them to life, Hollywood-style, with sets and props meticulously constructed, the lighting, sound, and camera positions established, and the first assistant director then commanding, “OK, lock it up,’’ as a signal to to halt all talk, movement, and traffic so that Cooper could call for action and shoot take after take until he liked the result.

To shoot a scene in the North End where FBI agents arrest the Mafia’s Jerry Angiulo at his 98 Prince St. office, set designer Stefania Cella converted an entryway just around the corner on Margaret Street into Angiulo’s headquarters. You could stand at the street corner, look one way to see the real deal, and then turn your head the other and see its mirror image. Whitey’s Lancaster Street garage is long gone, but Cella and her location scouts spotted a rundown garage down the street that somehow had survived the neighborhood’s redevelopment. They went to work and turned it into a gritty facsimile of the real one.

Siena Miller (left) plays the mobster’s moll, Catherine Greig.

These were the same streets — in the North End, around North Station, throughout Southie, and elsewhere — where years ago I and other reporters gathered information and context for stories about Whitey and the FBI. Now they were being reworked and reborn into a film adaptation of that epic saga.

Between takes one day in South Boston, Joel Edgerton, hair coiffed and dressed to the nines in the style of John Connolly, was making small talk, but there was no trace of his native Aussie accent, only Connolly’s Boston brogue. Meanwhile, Benedict Cumberbatch, newly arrived from London, was huddled in the backyard resuming his lessons with dialect coach Howard Samuelsohn, and Benedict emerged talking like Whitey’s younger brother, former state Senate president Bill Bulger, with the unmistakable Irish lilt Bulger liked to roll out as a garnish on public occasions. Rory Cochrane, as Stevie Flemmi? He never seemed to break character, at least not when I was watching. He stood around during breaks, barely talking to anyone, chain-smoking, brooding, and creepy-looking. It was unnerving, as Capote said, ghosts walking in sunlight.

There was the scene, too, where the script calls for two Globe reporters named Lehr and O’Neill to meet with an FBI source at a busy restaurant. The director cast two actors to play us but then offered Gerry O’Neill and I a cameo. We were seated at the nearest table, two guys dining next to the reporters and their source. We were ordered not to make a sound because the microphones pick up everything. “Just keep mouthing the words peas and corn,” Cooper said, explaining that the words make your face move as in conversation.

Who knew pretending could be so hard? I’m not sure which odd couple found this scene weirder — Gerry and me, or the actors trying to be us while we scrutinized their every move.

Filming wraps in Boston Friday, and what a long and winding road it’s been. The Globe first broke the story about Whitey’s ties to the FBI in 1988. “Black Mass” was published in 2000.

Now comes the movie, more than another decade later, following countless false starts that are apparently the norm for Hollywood.

The question is regularly asked: Is the movie a literal adaptation? The answer is no, and when you think about it, what movie adaptation is? Steven Spielberg’s historical drama “Lincoln”? Ben Affleck’s “Argo”? Just as in those great films, characters and events in the movie version of “Black Mass” are being compressed, and dialogue is invented. Scott Cooper has his script, but the actual filming is a dynamic process. He encourages actors to improvise, like in the “Officer Flynn’’ scene where Whitey gets pulled over by that Boston cop on Angiulo’s payroll. The cop has stopped Whitey to issue a warning for roughing up an Angiulo enforcer.

“Look what crawled out of the gutter,’’ he greets Whitey. The two size each other up, and the script next calls for Whitey to say, “You wouldn’t be carrying a message, would you?’’ With the camera rolling, and after several takes doing just that, Johnny’s Whitey pauses, and he adds a word — pigeon. “You wouldn’t be carrying a message, would you?” Pause. “Pigeon.’’ One word, spoken with loathing and loaded with subtext, since Whitey himself was a betrayer, an FBI rat. It’s pitch perfect, and, watching from their respective perches, Cooper and the producers smile.

John Tlumacki/Globe Staff

Palm trees were planted on Revere Beach in a scene in which Whitey Bulger and his gang take a break from the underworld grind in Miami.

What comes across most of all is authenticity, and the crew’s obsession with achieving it while dramatizing Whitey’s world, where a crime boss and killer becomes an FBI informant and masterfully turns the tables, so that lawbreaking FBI agents become his protectors. That concept is intact — a black mass of dark venality that harmed the bureau, Southie, all of Boston, and justice itself.

This authenticity becomes evident in moments big and small. On Revere Beach, for example, during that long day of filming into night, the scene calls for Whitey and his gang to reconvene in a seedy Little Havana bar. The set has been lit, there’s a full moon over “Miami.” The Bulger gang is all business, focused on Whitey’s agenda of killing Roger Wheeler of Tulsa, Okla., president of World Jai Alai, so that the mobster can continue skimming millions from the company’s sports-betting jai alai frontons in Florida and Connecticut.

Whitey is fully in command, cold and calculating. In a close-up, there’s that terrifying look in his eyes. When the director yells, “Cut,’’ the filmmaking spell may be broken, but everyone viewing in the video tent stays quiet, still mesmerized, as a big chill lingers from the scene just finished a few yards away.

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